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====Viral Family====

====Family Togaviridae====

Members of the Togaviridae are small, lipid- and protein-enveloped RNA viruses.  Within this family are disease-causing arboviruses (insect-borne virsuses) of the ''Alphavirus'' genus.

Small, lipid- and protein-enveloped RNA viruses.  The family includes pathogenic arboviruses (insect-borne virsuses) of the ''Alphavirus'' genus.

====Viral Genus====

====Genus Alphavirus====

Alphaviruses are single-stranded, linear, positive-sense RNA viruses, 60-70nm in diameter.

Single-stranded, linear, positive-sense RNA viruses, 60-70nm in diameter.

[[Image:Alphavirus.gif|300px|thumb|right|''' (Surface of an Alphavirus.  This image is a computer-generated model of the surface of an alphavirus derived by cryoelectron microscopy. The spike-like structures on the virion surface are trimers composed of heterodimers of the virion surface glycoproteins E1 and E2. These spikes are used by the virus to attach to susceptible animal cells.  ''Sourced from Wikimedia Commons, Copyright of the Centers for Disease Control and Prevention (CDC) Division of Vector-Borne Infectious Diseases, 2007)'' ''']]

[[Image:Alphavirus.gif|300px|thumb|right|''' (Surface of an Alphavirus.  This image is a computer-generated model of the surface of an alphavirus derived by cryoelectron microscopy. The spike-like structures on the virion surface are trimers composed of heterodimers of the virion surface glycoproteins E1 and E2. These spikes are used by the virus to attach to susceptible animal cells.  ''Sourced from Wikimedia Commons, Copyright of the Centers for Disease Control and Prevention (CDC) Division of Vector-Borne Infectious Diseases, 2007)'' ''']]

====Important Serotypes====

====Important Serotypes====

During equine and human epidemics of encephalitis in the Western Hemisphere, the most frequently isolated alphaviruses have included:

Several alphavirus strains have been isolated during equine and human epidemics of encephalitis in the Western Hemisphere.  These epidemics have most often been attributed to:

*[[Equine Togaviral Encephalitis|Eastern Equine Encephalitis virus (EEV)]]

*[[Equine Togaviral Encephalitis|Eastern Equine Encephalitis virus (EEV)]]

*[[Equine Togaviral Encephalitis|Western EEV]]  

*[[Equine Togaviral Encephalitis|Western EEV]]  

*[[Equine Togaviral Encephalitis|Venezuelan EEV]]

*[[Equine Togaviral Encephalitis|Venezuelan EEV]]

EEE and WEE are specific and discrete species.  There are North and South American antigenic variants of EEE.  WEE is a recombinant between an EEE-like virus and a Sindbis-like virus.  There are two antigenic subtypes of WEE virus: WEE and Highlands J viruses.  Extensive geographical overlap occurs between the various strains which have equivocal differences in antigenic properties and biological behaviour.  There are 6 distinct subtypes of VEE virus.  Over the last 20 years, large outbreaks of equine encephalitis in the Western Hemisphere have been caused by subtypes IAB, IC and IE.  ID and IF variants from Central America and Brazil respectively, type II (Everglades) virus in Florida and types II, IV, V ad VI viruses are considered endemic and are of low pathogenicity for horses under most circumstances.

Eastern EEV has North and South American antigenic variants.  Western EEV is a recombinant between an Eastern EEV-like virus and a Sindbis-like virus.  Western EEV also has two antigenic subtypes - WEE and Highlands J viruses.  Considerable overlap exists between the various strains in terms of their geography, and potentially also in their antigenic properties and biological behaviour.  Of the 6 subtypes of Venezuelan EEV (I-VI), significant outbreaks of equine encephalitis in the Western Hemisphere over the last two decades have been caused by IAB, IC and IE.  Variant ID from Central America and variant IF from Brazil are considered endemic and typically demonstrate low pathogenicity for horses.  These features are also typical of subtype II (Everglades) virus in Florida and types II, IV, V ad VI viruses.

====Diseases====

====Diseases====